Oxygen is crucial to sustaining life. Though it varies from person to person, on an average, 3 minutes is the maximum time where the person can stay alive without oxygen. Yoga and meditation experts may hold breath for longer than this, but these are very rare examples. In an absence of oxygen, brain cells begin to die and this effect is irreversible!
You can live 3 minutes without air, though I don’t recommend trying.
In a harsh environment — it’s snowing, say — you have 3 hours to survive without shelter. After 3 days, you need water or you’ll perish. You can make it 3 weeks without food, though promise you that won’t be fun.
How long can the brain go without oxygen before serious damage occurs?
After five to ten minutes of not breathing, you are likely to develop serious and possibly irreversible brain damage.